What did Sarei Yehudah hear?
Rashi: That the false Nevi'im and Kohanim had seized Yirmeyah.
Malbim: (They heard that the Am wanted to kill him not according to Torah law.) The Sarim did not want to spill innocent blood, so they investigated whether he is Chayav Misah according to Torah law. The Am departed, for they believed that he is a true Navi, and one cannot kill him according to law.
Why is it called "Sha'ar Hashem he'Chadash"?
Rashi: Later, the name was changed. When Yehoyachin was exiled, and some Kelim of Beis Elokeinu with him, Nebuchadnetzar's army broke the eastern gate. Tzidkiyah fixed it and renewed it, therefore it is called Chadash.
Radak citing Yerushalmi Eruvin 5:1: It is the eastern gate, like Yonason translates. It had seven names 1 . It is called Sha'ar Chadash, for there Chachamim were Mechadesh a Halachah (that a Tevul Yom may not enter the Ezras Nashim).
Radak: Perhaps they renewed it, or added something new to the building 2 .
Even though Hashem dictated the size of everything in the Mikdash ("bi'Chsav mi'Yad Hashem Alai Hiskil" - Divrei ha'Yamim I, 28:19), one can add to them via a king, Navi, Urim v'Tumim, Sanhedrin of 71, two Todos and Shir (Shevu'os 16a). (PF)
